That's a good one.  I'll have to make coffee first, but, `apply(c: Iterable[T])` is usual and `apply(c)` usually suffices because Iterable is more specific than TravOnce. That only works with the upper bound on `apply[T](t: T*)` and not without it, since otherwise it would take T as `Seq[T]`, which goes to the previous remark about overloading with `T*`.